Generalized Multiprotocol Label Switching (GMPLS) is a type of protocol which extends multiprotocol label switching (MPLS) to encompass network schemes based upon time-division multiplexing (e.g. SONET/SDH, PDH, G.709), wavelength multiplexing, and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). Multiplexing is when two or more signals or bit streams are transferred over a common channel.
Wave-division multiplexing is a type of multiplexing in which two or more optical carrier signals are multiplexed onto a single optical fiber by using different wavelengths (that is, colors) of laser light.
Lightpaths, or optical channels, are optical connections carried over a wavelength, end to end, from a source node to a destination node in an optical network. Typically, the lightpaths pass through intermediate links and intermediate nodes in the network. At the intermediate nodes, the lightpaths may be routed and switched from one intermediate link to another intermediate link. In some cases, lightpaths may be converted from one wavelength to another wavelength at the intermediate nodes.
A switched network usually includes multiple switch nodes (also referred to as “nodes”) which are connected by communication links. Within the network, user traffic can be transported between any two locations using predefined connections specifying particular links and/or switch nodes for conveying the user traffic.
An exemplary optical communication network may contain multiple optical nodes, such as optical line terminals (OLTs), optical crossconnects (OXCs), optical line amplifiers, optical add/drop multiplexer (OADMs) and/or reconfigurable optical add/drop multiplexers (ROADMs), interconnected by way of intermediate links. OLTs may be used at either end of a connection or intermediate link. OADM/ROADMs may be used to add, terminate and/or reroute wavelengths or fractions of wavelengths. Optical nodes are further described in U.S. Pat. No. 7,995,921 titled “Banded Semiconductor Optical Amplifiers and Waveblockers” and U.S. Pat. No. 7,394,953 titled “Configurable Integrated Optical Combiners and Decombiners”, which are incorporated herein by reference in their entirety.
An exemplary optical communication network contains multiple “layers” such as electronic and optical layers. The electronic layer includes an optical channel transport unit (OTU) sub-layer and an optical channel data unit (ODU) sub-layer. The optical layer has multiple sub-layers, including the Optical Channel (OCh) layer (an OCh may contain one or more optical carriers), the Optical Multiplex Section (OMS) layer, and the Optical Transmission Section (OTS) layer. The optical layer provides optical connections, also referred to as optical channels or lightpaths, to other layers, such as the electronic layer. The optical layer performs multiple functions, such as monitoring network performance, multiplexing wavelengths, and switching and routing wavelengths. The Optical Channel (OCh) layer manages end-to-end routing of the lightpaths through the optical transport network (OTN). The Optical Multiplex Section (OMS) layer network provides the transport of optical channels through an optical multiplex section trail between access points. The Optical Transmission Section (OTS) layer network provides for the transport of an optical multiplex section through an optical transmission section trail between access points. The OCh layer, the OMS layer, and the OTS layer have overhead which may be used for management purposes. The overhead may be transported in an Optical Supervisory Channel (OSC).
The Optical Supervisory Channel (OSC) is an additional wavelength that is adapted to carry information about the network and may be used for management functions. The OSC is carried on a different wavelength than wavelengths carrying actual data traffic and is an out-of-band channel. Typically, the OSC is used hop-by-hop and is terminated and restarted at every node. The International Telecommunications Union (ITU) recommendation ITU-T G.709 further defines the OTS, OMS and OCh layers and recommends use of the OSC to carry overhead corresponding to the layers.
Typically, current systems use out-of-band communication channels (that is, a different wavelength than the wavelength carrying user data traffic) such as the Optical Supervisory Channel (OSC) to carry information about the network and for management functions. However, the OSC may not be available, or reliability of the system may be improved by redundant communication channels. Therefore, an in-band channel is needed to carry overhead information through an optical connection, such as from a source node to a destination node, such that the overhead information can still be accessed without accessing or affecting the payload data.
The present disclosure addresses these deficiencies with methodology and apparatuses for modulating one or more optical carriers to carry additional data in-band between a source node and a destination node in a network. The method may utilize a format of a soft decision forward error correction (SD-FEC) data field of an overhead portion of a data frame and encode additional data into the SD-FEC data field, along with SD-FEC data. The additional data being accessible without accessing user data traffic.